1. Field of the Invention
The present invention relates to a position controller and position control method of an optical system for focusing converged light on an optical recording medium and a recording/reproducing apparatus for recording or reproducing information by focusing converged light on an optical recording media and a driving method of the same.
2. Description of the Related Art
As an optical apparatus, there are, for example, a recording/reproducing apparatus for recording or reproducing information using an optical disk or other optical recording medium, an optical microscope, etc.
A cut-off spatial frequency fc in an optical apparatus is generally expressed by formula (1) below by using a numerical aperture NA of an object lens and a wavelength A of an output light from a light source.
fc=2NA/xcexxe2x80x83xe2x80x83(1)
The shorter the wavelength xcex of light from the light source and the larger the numerical aperture NA on the object lens, the higher the resolution, so recording at a high density becomes attainable in a recording/reproducing apparatus and detailed observation becomes attainable in an optical microscope.
As a method of increasing the numerical aperture NA of an object lens, there is known a near-field optical system using a solid immersion lens (SIL). An optical system having a numerical aperture exceeding xe2x80x9c1xe2x80x9d has been attained by this method.
As a reference regarding a near-field optical system and a solid immersion lens, there is S. M. Mansfield, W. R. Studenmund, G. S. Kino, and K. Osato, xe2x80x9cHigh-numerical aperture lens system for optical storagexe2x80x9d, Opt. Lett. 18, pp. 305-307 (1993) (hereinafter referred to as xe2x80x9cReference 1xe2x80x9d).
Also, as another reference, there is, for example, H. J. Mamin, B. D. Terris, and D. Rugar, xe2x80x9cNear-field optical data storagexe2x80x9d, Appl. Phys. Lett. 68, pp. 141-143 (1996) (hereinafter referred to as xe2x80x9cReference 2xe2x80x9d).
Note that the U.S. Pat. Nos. 4,183,060 and 4,300,226 disclose detecting a distance between an optical disk and an electrode by a capacitance sensor, however, do not describe a near-field optical system and a solid immersion lens (SIL).
Japanese Unexamined Publication (Kokai) No. 8-212579 discloses an invention of an optical head and an optical recording medium. In this publication, an object lens is held by a lens holder, a solid immersion lens is held by a second lens holder, and position control of the solid immersion lens is carried out based on an electrostatic capacitance between the second lens holder and the optical disk using a conductive material for the second lens holder.
In a near-field optical system, it is necessary to keep the distance (air gap) between the optical system and the optical recording medium. within the range wherein the near-field is formed (near-field range) in order to focus light effectively on the optical recording medium.
Especially, when the numerical aperture exceeds 1, if the air gap becomes larger than the near-field range, the intensity of the light on the optical recording medium largely declines due to multi-reflection and interference of light between the optical system and the optical recording medium, so it is important to keep the air gap within the near-field range.
However, when bringing the optical system close to the optical recording medium from outside the-near-field range to within the near-field range to realize an air gap wherein a near-field is formed, for example, not more than 500 nm (preferably, an air gap of not more than 100 nm), there is the possibility that the optical system and the optical recording medium will contact or collide due to overshoot.
If the optical recording medium is rotating when the optical system and the optical recording medium contact or collide, friction will arise between the optical system and the optical recording medium and the area of contact on the surface of the optical recording medium becomes larger concentrically and circularly.
An object of the present invention is to provide a position controller and position control method of an optical system capable of effectively focusing light from a near-field optical system to an optical recording medium, a recording/reproducing apparatus, and a driving method.
Another object of the present invention is to provide a position controller and a position control method of an optical system capable of keeping the contact area and impact small when an optical system and an optical recording medium contact or collide at the time of shortening the distance between the optical system and the optical recording medium for forming a near-field.
Still another object of the present invention is to provide a recording/reproducing apparatus for recording or reproducing information by focusing light from a light source to an optical recording medium via an optical system capable of keeping the contact area and impact small when the optical system and the optical recording medium contact or collide at the time of shortening the distance between the optical system and the optical recording medium for forming a near-field and a driving method.
According to a first aspect of the present invention, there is provided a position controller of an optical system comprising an optical system for forming a near-field with an optical recording medium and focusing converged light to the optical recording medium; an actuator for moving the optical system in a focal direction perpendicularly intersecting a recording surface of the optical recording medium; and a control circuit for controlling the actuator so as to shorten the distance between the optical system and the optical recording medium from outside to inside the range where the near-field is formed and further maintain it inside the range.
Preferably, the control circuit controls the actuator so as to shorten the distance between the optical system and the optical recording medium in stages from outside to inside the range where the near-field is formed and further maintain it within the range.
More preferably, the control circuit controls the actuator to set the distance to an intermediate target value from an initial setting outside of the range, temporarily maintain it at the intermediate target value or substantially the intermediate target value, and bring it close from the intermediate target value to a final target value inside of the range.
The position controller further preferably comprises a motor for rotating the optical recording medium; the control circuit generating a starting signal after the distance is kept inside the range; and the motor starts to rotate the optical recording medium based on the starting signal.
More preferably, the position controller further comprises a laser for supplying a laser beam to the optical system after the optical recording medium rotates.
Preferably, the optical system comprises a first optical system having an object lens for converging light and a solid immersion lens for converging light passing through the object lens and focusing it on the optical recording system or a second optical system wherein the object lens and the solid immersion lens are made integral.
More preferably, the optical recording medium is an optical disk; the solid immersion lens has a central portion on a surface facing the optical disk which projects out, has a peripheral portion which is flat and formed with a conductive film, and converges light passing through the object lens and passes it through the central portion; and the control circuit controls the actuator based on an electrostatic capacitance between the conductive film and the optical disk to adjust the distance.
Preferably, the numerical aperture of the optical system is larger than 1 and equal or smaller than 3; and a range wherein the near-field is formed is a range wherein the optical system and the optical recording medium are in a non-contacting state and the distance is 500 nm or less.
According to a second aspect of the present invention, there is provided a position control method of an optical system for controlling a distance from an optical system for forming a near-field with an optical recording medium and focusing converged light to the optical recording medium to the optical recording medium, including the steps of shortening the distance between the optical system and the optical recording medium from outside to inside a range where the near-field is formed and maintaining the distance within the range.
Preferably, the distance is shortened in stages from outside to inside the range where the near-field is formed.
More preferably, the shortening step includes the steps of setting the distance from an initial setting outside the range to an intermediate target value and maintaining it at the intermediate target value or substantial intermediate target value and making the distance from the intermediate target value to a final target value inside the range.
The position control method preferably further includes a step of rotating the. optical recording medium after the distance is maintained inside the range.
The position control method preferably further includes a step of supplying a laser beam to the optical system after the optical recording medium is rotating.
Preferably, the numerical aperture of the optical system is larger than 1 and equal or smaller than 3 and the range wherein the near-field is formed is a range wherein the optical system and the optical recording medium are in a non-contacting state and the distance is 500 nm or less.
According to a third aspect of the present invention, there is provided a recording/reproducing apparatus comprising a light source; an optical system for forming a near-field with an optical recording medium, converging a light from the light source, and focusing it to the optical recording medium; an actuator for moving the optical system in a focal direction perpendicularly intersecting a recording surface of the optical recording medium; a control circuit for controlling the actuator so as to shorten the distance between the optical system and the optical recording medium from outside to inside the range where the near-field is formed and further maintain it within the range; a motor for rotating the optical recording medium at the time of recording information and reproducing information; an intensity modulation circuit for modulating a light intensity from the light source in accordance with recording information at the time of recording information; and a detection circuit for detecting recording information from reflection light reflected on the optical recording medium at the time of recording.
Preferably, the control circuit controls the actuator so as to shorten the distance in stages from outside to inside a range where the near-field is formed and maintain it within the range.
More preferably, the control circuit controls the actuator to set the distance to an intermediate target value from an initial setting outside of the range, temporarily maintain it at the intermediate target value or substantially the intermediate target value, and bring it close from the intermediate target value to a final target value inside of the range.
Preferably, the control circuit generates a starting signal after the distance is kept inside the range, and the motor starts to rotate the optical recording medium based on the starting signal.
Preferably, the light source is a laser for outputting a laser beam to the optical system after the optical recording medium is rotating.
Preferably, the optical system comprises a first optical system having an object lens for converging light from the light source and a solid immersion lens for converging light passing through the object lens and focusing it on the optical recording system or a second optical system wherein the object lens and the solid immersion lens are made integral.
Preferably, the optical recording medium is an optical disk; the solid immersion lens has a central portion on a surface facing the optical disk which projects out, has a peripheral portion which is flat and formed with a conductive film, and converges light passing through the object lens and passes it through the central portion; and the control circuit controls the actuator based on an electrostatic capacitance between the conductive film and the optical disk to adjust the distance.
Preferably, the numerical aperture of the optical system is larger than 1 and equal or smaller than 3 and a range wherein the near-field is formed is a range wherein the optical system and the optical recording medium are in a non-contacting state and the distance is 500 nm or less.
According to a fifth aspect of the present invention, there is provided a method of driving a recording/reproducing apparatus using an optical system forming a near-field with the optical recording medium to focus converged light on an optical recording medium for recording or reproducing information, including the steps of shortening the distance between the optical system and the optical recording medium from outside to inside a range where the near-field is formed; maintaining the distance within the range; rotating the optical recording medium; detecting recorded information from reflection light reflected at the optical recording medium during rotation at the time of reproducing information; and supplying modulated light modulated in intensity in accordance with recording information and focusing converged light from the optical system to the optical recording medium during rotation.
Preferably, the distance is shortened in stages from outside to inside a range where the near-field is formed.
Preferably, the shortening step includes the steps of setting the distance from an initial setting outside the range to an intermediate target value and maintaining it at the intermediate target value or substantial intermediate target value and making the distance from the intermediate target value to a final target value inside the range.
Preferably, the optical recording medium is rotated after the distance is maintained inside the range.
The method preferably further includes a step of supplying a laser beam to the optical system after the optical recording medium is rotating.
Preferably, the numerical aperture of the optical system is larger than 1 and equal or smaller than 3 and the range wherein the near-field is formed is a range wherein the optical system and the optical recording medium are in a non-contacting state and the distance is 500 nm or less.